In the transfer of a design or picture to the surface of a ceramic article or like base product, it is common practice to use a water slide technique. According to the technique, a water-soluble size or paste layer is first formed on a release paper, a multicolor picture layer is formed thereon and, where necessary, a picture-supporting layer is further disposed on the picture layer to provide a transfer sheet. In transfer printing, the thus-obtained transfer sheet is wetted with water to dissolve out the water-soluble size and, hence, let the picture layer leave from the release sheet, whereupon the picture layer is slide-transferred to the surface of a ceramic or other substrate. Then, using a squeegee and like tools, water between the picture layer and the substrate ware is squeezed out. The substrate ware is allowed to stand for drying the picture layer. After completion of drying, the ware is calcined at as high as about 1000.degree. C. to permanently fix the design or picture thereto.
However, this technique has the disadvantage that since a step for high-temperature calcining at about 1000.degree. C. is essential, the use of heat-labile coloring materials, which are rich in colors, color tones, etc., is limited. Further, because the squeegee and like tools are essentially used in the technique, the manual labor of skillful operator is required, thereby increasing the production costs.
Japanese Unexamined Patent Publication 252,600/1990 discloses "a transfer sheet comprising a release paper or film base carrying thereon a water-soluble size or releaser, a supporting layer disposed on said base and capable of maintaining the shape of a picture layer to be transferred and, as formed thereon, a picture layer comprising a printing layer selected having a B stage so as to insure a greater bond strength with respect to a substrate ware than the bond strength to said supporting layer" and a transfer process employing said transfer sheet.
In the process, calcining or curing the printing layer is performed at a temperature of 80.degree.-300.degree. C. and, therefore, the above-mentioned problem associated with high-temperature calcination is overcome. However, when the process is applied to multicolor decalcomania, it takes a long time for the printing layer to establish the B stage, with the result that the efficiency of production of the transfer sheet is inevitably low.
Furthermore, when the printing layer is calcined at a relatively low temperature of 80.degree.-170.degree. C., a sufficient degree of cure can be achieved only after prolonged heating leading to an inadequate adhesion of the printing layer to the substrate ware. There also is the disadvantage that the water resistance of the picture to water, in particular, to warm water is low.
It is a primary object of the invention to provide a novel transfer sheet which permits the use of heat-labile coloring materials and enables multicolor decalcomania at a comparatively low temperature without procedural complexity.
It is a further object of the invention to provide a novel transfer process which affords multicolor decalcomania at a comparatively low temperature without procedural complexity.
Other objects and advantages of the invention will become apparent in view of the following description.